The overall goal of the study is to investigate the mechanisms whereby brain hypoxia alters the control of breathing. Special emphasis is on interrelationships of brain blood flow and control of breathing. For the coming year we plan to study the chemical and neuropharmacological control of brain blood flow during sleep. In goats we will assess the effects of sleep stage on total brain blood flow with and without hypoxia and hypercapnia (increased CO2 level). The preparation will allow evaluation of the time course of the effects of sleep, hypoxia, hypercapnia and combinations of the three. In cats we will use a static measurement to assess the effects of sleep with and without hypoxia and hypercapnia on regional brain blood flow. In cats we will assess the role of dopamine in setting regional brain blood flow and O2 consumption during hypoxia. Finally, we will assess the effects of chronic hypoxia on the way in which acute hypoxia causes arousal from sleep.